This invention relates to apparatus for the administration of anesthesia, and more particularly to apparatus for preventing unwanted pressure build up in the patient anesthesia circle.
A conventional method for administration of gaseous anesthesia features the so-called patient anesthesia circle, wherein oxygen and the anesthetic gases are coupled to the patient for inhalation, and exhaled gases are passed through a carbon dioxide absorber and back to the entry point of oxygen and anesthesia. One way valves isolate the patient from the source of anesthesia and the carbon dioxide absorber, and a reservoir bag is provided on the patient side of the valves. In such a system, it is important to provide apparatus in the circle to prevent pressure build-ups which may be harmful or fatal to the patient. To this end, pressure relief valves conventionally are included, which are designed to open the system to the atmosphere when pressure exceeds a predetermined threshold. The most common designs of such valves feature diaphragms or pistons which are held in place by the force of a spring. When pressure in the circle is sufficient to deflect the spring, the diaphragms or pistons are displaced, and pressure is relieved.
More recently, attention has been given to the fact that such pressure relief expells anesthesia gases into the atmosphere, and undesirably exposes operating room personnel thereto. Hence, vacuum exhausts have been developed whereby gases which are expelled from the anesthetic circle during excess pressure times are conveyed safely out of the operating room. Vacuum exhaust systems have complicated and accentuated difficulties which sometimes occurred in the operation of conventional pressure relief valves. In some cases, the diaphragms stick closed, allowing for the dangerous condition of hyperinflation of the patient. Also, the vacuum pressures often cause diaphragms or pistons to vibrate badly. Such vibration not only is annoying to the staff and accelerates wear of the valve, but more dangerously may impress oscillation on the system pressure, which also may be quite detrimental to the patient.
It is accordingly a primary object of the present invention to provide pressure relief apparatus for the patient anesthesia circle which functions synergistically with the vacuum exhaust, which avoids the problems of vibration and oscillation, and which will not stick in use.